A produce tray is a container for agricultural produce such as fruit and vegetables. Many different sizes and shapes of produce trays are available. Produce trays, also referred to as a produce tills, protect their contents during shipping and handling by preventing contact between the produce within and foreign contaminants, sealing the contents to maintain freshness, and limiting crushing and bruising damage to the produce. Damaged or contaminated produce may have reduced economic value, impaired flavor, poor visual appeal, or present health risks to consumers. A produce tray may be sealed with a polymer film attached to the top of the tray by heat welding, ultrasonic welding, or by a sealing band. Some produce trays use a snap-on cover. Other produce trays have a clamshell cover formed as part of the tray.
A bulk supply of agricultural produce may be subdivided into smaller portions and loaded into produce trays in a continuous process. Produce trays to be filled may be placed on the input end of a conveyer comprising one or more continuous belts, chains, or moving frames. The conveyor may have shaped apertures, pockets, cleats, pins, etc. to hold produce trays securely and with a predetermined tray-to-tray spacing. The conveyer moves produce trays to sequential processing stations, for example hoppers for transferring produce to individual produce trays, equipment for closing loaded produce trays, weighing equipment, and so on. Filled and sealed produce trays are removed from the output end of the conveyor. Conveyers known in the art are configured to hold a selected size and shape of produce trays and may need substantial modification to hold trays having a different size and shape.
Produce trays may be filled with a weighed portion of agricultural produce. A large amount of air may be trapped between pieces of produce in a weighed portion. For example, about half of the volume of a mound formed by dumping a portion of leafy vegetables such as spinach or lettuce into a produce tray may be air trapped in spaces between leaves. Because of the trapped air or because pieces of produce may be dumped into a disorganized mound in the tray, the top of the mound may extend above the top of the tray. Before sealing a produce tray it may therefore be necessary to compress the produce in the tray until the top of the mound is below the top of the tray.
A plunger may be used to compress the mound of produce in a tray or workers may apply hand pressure to compress the mound. A plunger may have a relatively flat compression face, i.e., the side of the plunger that contacts produce in a tray. Produce may adhere to a flat compression face when the plunger is removed from a tray, possibly resulting in underweight portions being sealed into produce trays, unwanted transfer of produce from one tray to another, or produce dropped on the floor. Produce may be blown out of a tray by air expelled during compression with a flat plunger. Produce trapped between an outer edge of a plunger and an interior side wall of a produce tray may be crushed or torn. Produce expelled from the tray during compression may fall on an upper surface of the produce tray and may interfere with sealing of the tray. Or, spilled produce may accumulate on the floor or on handling equipment and must be cleaned up to prevent safety and sanitation problems.
A mound of produce dumped in a tray is usually higher toward the center of the tray than near the tray edges. A flat plunger may over-compress the raised center of the mound and cause bruising or crushing of some of the produce in the tray. Some plungers have stepped compression faces to reduce adhesion by surface tension and suction between the plunger's compression face and pieces of produce. Plungers with stepped compression faces may have improved performance compared to plungers with flat compression faces, but problems associated with produce adhesion, over-compression, and expulsion of produce by spillage and airflow during produce compression remain. More than one compression operation may be needed before tray sealing since produce compressed with either a flat or stepped plunger may re-expand to a substantial fraction of its original volume after each compression step. For example, some agricultural produce approximately doubles in volume after being compressed by a flat or stepped plunger. It may therefore be necessary to install more than one compression station along a conveyor, resulting in increased amounts of damaged produce and higher equipment cost, facility cost, and operating cost. It may also be necessary to have workers monitor produce trays after each compression step and manually finish each tray. Each additional person needed for tray processing not only raises labor costs but introduces additional risk of human injury from working in close proximity to moving machinery and risk of biological contaminants being transferred from workers to food in produce trays.